If both LEDs are lit then either the LEDs are not opposed as they should be, or the circuit is oscillating at a high frequency (instead of a low one).

So first check the LEDs - are you sure one is facing this way and one that way?

Second, look at the op-amp with the 1uF cap in its feedback loop. It is the integrator. Find the - input of that op-amp. It should be getting fed via a network of resistors/diodes/pots from the output of another opamp. Measure the resistance of that network from the output of one op-amp to the - input of the integrator. Resistance should be approx 100K.

Third, check that all the pins that should be at 0V are actually at 0V. The + input of the integrator especially. And the pots that should have one side at 0V. Check all those points with the circuit running to make sure they are all really at 0V exactly.

Thanks for the replies & ideas... I think the problem was that I had it on the same board as my ADSR (which isn't working either; see that thread!) and that has electro caps on the +/- power. I built the LFO all by itself and it works perfectly

I'm working on a "rack monosynth" and am now going to build three of these LFOs and have them normalled to the FM and PWM of my JH Living VCOs. Massive...

he!
I build the VCLFO and the LFO from nicolas on one board. This circuit rules!!!
It's a nice patch if you plug the saw out of the "normal LFO" at a very slow rate to the CV input of the VCLFO. So the VCLFO output is getting faster and faster then slower and slower and faster adn fsater nda slower adn sowler...
that's exactly what I needed and it works!

The next module will be the ADSR Generator.
Biggest thanks for this one nicolas3141

I hope it's alright that I'm reviving this thread. Those LFO's just look very useful for what I'm planning to do. Especially since I have quite a few LM324's kicking around.
I just wanted to know if the first one can be adapted to a single 5V supply as easily as to 9V.
Also, for using it to control resistance, would you rather suggest to run its output into a Vactrol or a Transistor?

Hi Tim. I'm reviving this 4 year old thread to ask you a question about your TSQ circuit.

I can't for the life of me figure out why you added that -V connection to the inverting input of the op amp. I've attached an analysis below that may interest people who are obsessive about rigour. I get a kick out of algebra

What is its purpose? I noticed that you kept R2 in the LFX schematic you posted, even though you revised the circuit in general. Something to do with op amp unidealities?

Wow, that's a neat analysis. However, the circuit really is fairly simple. It is just a non-inverting buffer, and the ratio of R3 to R1 determines the gain. The circuit is set so that at the maximum setting of R1 (at the 'triangle' setting), the triangle wave comes through at its original amplitude and shape. As R1 is reduced, the negative feedback into the "-" pin is reduced (more of it is shunted to ground) and the gain increases, and as the output amplitude rises it starts to bump up against the output 'rails' which causes the peaks to flatten off. R4, R5 and R6 take what is a +/-12V wave and reduce it to a standard +/-5V. You could probably tweak the value of R5 a bit (reduce it) and actually get rid of R4. The purpose of R2 is simply to introduce a teeny DC bias to make the output centered around 0V. This was a value derived just from simple experimentation, and it's what worked with the op-amp I was using at the time. You may need a slightly different value.

Bah, I was too ambitous and tried to build 2 into 1 pedal box with just one 9V battery, seems like thats not enough to drive them.
The virtual ground and such does work, but with 2 the voltages are off at the input, 1 of them seems to do all it should as well, blinking slightly on one led in time and giving off a small but correct waveform, but the other hangs, and both get -6.3V and +3.1
However even when disconnecting the other, the working one only gets +/- 5V. Waveforms go between +/- 1V.
I did what was suggested, replaced leds with green, changed resistor to 47K, and used 2 more 10uf electrolytic caps negative leg to negative V input, positive to positive V, and the others to virtual ground.

Now, they are cheap batteries, but Ive run a MFOS mini synth fine off two of them, so they should have more than enough juice really?
The potential of the battery is 9.5ish, so it looks more like it divides unequally or equally, but doesnt give out 9v on both?
Is that how the virtual ground works or something?

why do people allways think it's bad to revive old threads? this thread is as good as it ever was and it was, as ever, pretty good!

I was going to contribute my LFO circuit but I can't find it now and it's not as good anyway but it has a lower parts count._________________As a mad scientist I am ruled by the dictum of science: "I could be wrong about this but lets find out"

I couldn't find the original schematic but I could pretty much remember everything, so I drew up another one.
There is another LFO of mine somewhere on this forum, but it's a simple 555 timer based thing, uses more parts than this one!

this one is, as it says, optimized for single supply operation.

GDAL LFO.png

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Forgot to add: +V is 12V

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7327 Time(s)

_________________As a mad scientist I am ruled by the dictum of science: "I could be wrong about this but lets find out"

While this replay is mainly for Nicolas, others feel free to chime in.

For a long time I was considering a build of the Variable Skew LFO circuit that is on the MFOS website. However, since that circuit no longer has a PCB for it, I am a bit at a loss of how to layout something like that on a strip board.

Low and behold doing a bit of searching it seems that Nicolas has made his own variant of the Variable Skew LFO that uses few parts AND has a strip board diagram.

But further down I noticed that Nicolas also created a VC-LFO variant, and that had me doing one of these The trouble with that LFO is the mentioned issue with the Skew control. I am curious if this issue was straightened out? If not, is there a fix for it by adding a few more parts?

Overall, down the road, I would be looking into a tracking VCO that has similar features to this. I would like the ramp-tri-saw adjustability in addition to 1v/Octave tracking. Further, I would be interested if something like this could also do double duty as an VCO / VC-LFO.

Oh! As of now my planned power supply is a +12 0 -12 running from AC.

Thank You,

Geo_________________Lover...I won't take a back seat, tonight. Got some dancin' to do.

Bah, I was too ambitous and tried to build 2 into 1 pedal box with just one 9V battery, seems like thats not enough to drive them.
The virtual ground and such does work, but with 2 the voltages are off at the input, 1 of them seems to do all it should as well, blinking slightly on one led in time and giving off a small but correct waveform, but the other hangs, and both get -6.3V and +3.1
However even when disconnecting the other, the working one only gets +/- 5V. Waveforms go between +/- 1V.
I did what was suggested, replaced leds with green, changed resistor to 47K, and used 2 more 10uf electrolytic caps negative leg to negative V input, positive to positive V, and the others to virtual ground.

Now, they are cheap batteries, but Ive run a MFOS mini synth fine off two of them, so they should have more than enough juice really?
The potential of the battery is 9.5ish, so it looks more like it divides unequally or equally, but doesnt give out 9v on both?
Is that how the virtual ground works or something?

I just prototyped this LFO and I'm very happy with it. I played with having two TSQ's with independent wave shaper pots - but the effect ended up being that the second pot also modifies the shape of the first wave adjust pot. I'm playing with making that a feature in my finished module. Hoping I can switch a second adjustment knob in and out.

The add-ons also seem to pollute the signal of the square and tri outs. Again - that adds to the uniqueness of this module. If you want perfect square and tri wave forms then there are plenty of other LFO's to build.

Point is, the circuit is functional and a good addition to my newbie rig.

- Kevin

Tim Servo wrote:

Here's a coupla add-ons for the 8K LFO. The first (TSW) uses the Tri and Square to make a Saw, or even a 2X Saw. The second (TSQ) takes a Tri and puts out a wave that is continuously variable from Tri to Square, with a "Trapezoid" shape in the middle. You can even take the output of the TSQ and put it into the TSW, and now you have a Tri to Square on one output and a Saw to Square on the other (both varied at the same time with the Waveshape control on the TSQ). By the way, a 1458 or other "low bandwidth" op amp works a little better for the TSW because it helps minimize the glitch in the reconstructed Saw output. I've got some more add ons that I'm still working on, but I thought I'd throw these out here because these variable outputs are so much fun.

I've built the Nicolas LFO on solderless breadboard. I'm getting 0V where I should be getting -V and I can't figure out why. It's running on 9V battery. Pin 4 reads 7.35V. Virtual Ground is 0V. All the pot lugs seem to be 0V. One LED briefly flashes, once, when I first connect the power, then goes out.
Anyone have any suggestions?

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